Lennox Furnace Manuals G20

The Lennox G20 Series is a high-efficiency gas furnace line featuring advanced heating technology, durable construction, and energy-saving performance. These furnaces offer AFUE ratings up to 96%, variable-speed blower motors, quiet operation, and compatibility with various thermostat systems. Below are essential sections covering safety, specifications, installation, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Durable heat exchanger, variable-speed blower motor, electronic ignition system, multi-speed inducer motor, and integrated control board.

Installation Guidelines

Professional installation recommended. Ensure proper location and clearances.

1. Location selection: Choose well-ventilated area with adequate clearance (minimum 1 inch sides, 6 inches front).
2. Gas connection: Use approved gas piping; pressure test for leaks before operation.
3. Electrical wiring: Connect to 120V AC power; follow local electrical codes.
4. Venting system: Install PVC vent pipes according to manufacturer specifications.
5. Ductwork: Ensure proper sizing and sealing for optimal airflow.

WARNING! Gas furnaces produce carbon monoxide; proper venting is critical. Only qualified technicians should perform installation.

First-Time Setup

Initial startup requires professional commissioning.

1. System check: Verify all connections, gas pressure, and electrical wiring.
2. Venting verification: Confirm proper draft and vent pipe installation.
3. Gas pressure adjustment: Set manifold pressure to specifications (typically 3.5" WC).
4. Blower speed configuration: Adjust dip switches for proper airflow.
5. Thermostat programming: Set up heating cycles and temperature settings.

CAUTION! Never attempt first-time startup without proper training and equipment.

Technical Specifications

• Model Series: G20Q, G20Q2, G20Q3
• Input BTU/H: 40,000 to 120,000
• AFUE Rating: 80% to 96%
• Gas Type: Natural Gas or LP (with conversion kit)
• Electrical: 120V AC, 60Hz, 1.5-3.0 Amps
• Blower Motor: ECM Variable Speed
• Static Pressure: 0.1 to 0.8 inches WC
• Venting: PVC, CPVC, or ABS (2-3 inch diameter)
• Operating Temp Range: -30°F to 120°F ambient
• Warranty: 20-year heat exchanger, 5-year parts

Controls and Settings

Integrated control board with LED status lights. Access via front panel or thermostat.

Control Board Features: Power indicator, status LED, dip switches for configuration, diagnostic codes.

Thermostat Settings: Heat mode selection, fan control (auto/on), temperature setpoints, system mode. Blower Settings: Adjustable speeds via dip switches for heating and continuous fan modes. Safety Controls: High limit switch, rollout switches, pressure switches, flame sensor.

Venting Requirements

Category IV venting system required. PVC, CPVC, or ABS piping.

1. Vent pipe sizing: 2-inch minimum diameter for most models.
2. Termination clearances: 12 inches from windows, doors, and air inlets.
3. Slope requirements: 1/4 inch per foot toward furnace for condensation drainage.
4. Combustion air: Provide adequate fresh air intake per local codes.

Tip: Always follow manufacturer venting tables for specific model requirements.

Operation Instructions

Normal operation via thermostat control.

1. Power on: Ensure electrical power and gas supply are connected.
2. Thermostat call: Set thermostat above room temperature to initiate heating cycle.
3. Sequence of operation: Inducer motor starts, pressure switch proves, ignition begins, gas valve opens, flame established.
4. Blower operation: Blower starts after heat exchanger warm-up period.
5. Cycle completion: System shuts down when thermostat satisfied.

WARNING! Never block air vents or returns; maintain clear airflow paths.

Maintenance Procedures

Regular maintenance ensures optimal performance and safety.

1. Monthly: Check and replace air filter as needed.
2. Annual: Professional inspection and cleaning.
3. Blower compartment: Clean annually, check motor and wheel.
4. Heat exchanger: Visual inspection for cracks or damage.
5. Vent system: Check for obstructions and proper drainage.

CAUTION! Always disconnect power before performing any maintenance.

Safety Information

Carbon monoxide detectors required in all living spaces. Never operate with suspected heat exchanger damage.

EMERGENCY SHUTOFF: Gas shutoff valve located at furnace; electrical disconnect switch required nearby.

Regulatory Compliance

UL certified; meets ANSI Z21.47 standards. CSA design certified. Complies with U.S. Department of Energy efficiency standards. For technical support, contact Lennox at 1-800-9-LENNOX or visit www.lennox.com.

Troubleshooting Guide

Reset: Power cycle furnace at electrical disconnect.

Service: 1-800-9-LENNOX; www.lennox.com